Matchmakers

QUANTUM cryptography and quantum teleportation could become easier thanks to a new way of spotting special photons, say scientists in Austria. The technique allows researchers to separate ordinary photons from those that are mysteriously "entangled" with a distant twin. "This separation is crucial for quantum communications," says Richard Hughes, a physicist at the Los Alamos National Laboratory in New Mexico.

Entangled photons are the Siamese twins of the quantum world. According to the laws of quantum mechanics, they are linked in such a fundamental way that carrying out a measurement on one determines the state of the other, no matter how far apart they might be. This ability to influence a distant photon by measuring one nearby is important for quantum communication.

But distinguishing entangled photons from ordinary ones is not easy. Until now, the most promising proposal has been to use the quantum equivalent of a logic gate, known ...

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